The major focus of this research group is the study of responses to genotoxic stress in mammalian cells. This has included the cloning and characterization of a variety of DNA-damage-inducible (DDI) genes and the role of p53 in their regulation. Studies have involved the gadd genes, BCL2, BAX, beta-polymerase, 06-methylguanine DNA methyltransferase, c-jun, c-fos, topoisomerases I and II, metallothionein, and ubiquitin. Understanding the role of DNA-damage responses in determining the cellular sensitivity to cytotoxic agents, such as used in cancer therapy, is a major objective. An important response to genotoxic stress in all cells are delays in cell cycle progression which are induced by DNA damage. These delays are mediated by various genes and probably include the gadd genes which are both DDI and growth-arrest inducible. The major portions of this project focus on: l) the study of the expression of the gadd genes and characterization of the cDNA and genomic clones for these five genes; 2) the role of the tumor suppressor p53 in mediating DNA damage responses; 3)the regulation of these genes with particular emphasis on gadd45; 4) the characterization of the gadd proteins with the development of high- affinity antibodies; 5) elucidation the function of these genes; 6) the role of the gadd and related genes in apoptosis; 7)the use of transgenic mouse models to study the roles of these genes in vivo; 8) the expression of these genes in human tumor cell lines with known sensitivity to various chemotherapy agents, such as the panel of lines from the NCI drug screening program. Of particular interest is our recent findings that the GADD45 gene is p53-regulated and the Gadd45 protein interacts with proteins involved in both cell-cycle regulation and DNA repair. The regulation of GADD45 and related proteins by p53 has have important implications in cancer therapy considering that approximately two thirds of human tumors lack normal p53 function.